Solutions of polymer semiconductors

ABSTRACT

The present invention relates to a process for producing particle-free solutions of polymeric semiconductors and to their use for producing layers of polymeric semiconductors in polymeric organic light-emitting diodes (PLEDs), organic integrated circuits (O-ICs), organic field effect transistors (OFETs), organic thin film transistors (OTFTs), organic solar cells (O-SCs) or organic laser diodes (O-lasers).

[0001] The present invention relates to solutions of polymericsemiconductors and their use in the electronics industry.

[0002] In a variety of applications, which in the broadest sense can beconsidered part of the electronics industry, the use of organicsemiconductors as active components (=functional materials) has beenreality for some time or is expected in the near future. Thus, chargetransport materials based on organic compounds (generally hole transportmaterials based on triarylamines) have been used in copiers for someyears.

[0003] The use of specific semiconducting organic compounds, some ofwhich are also capable of emitting light in the visible region of thespectrum, is just beginning to be introduced on the market, for examplein organic or polymeric electroluminescence devices.

[0004] The use of organic charge transport layers in applications suchas organic integrated circuits (organic ICs) and organic solar cellshas, at least in the research stage, progressed so far that introductionon the market within the next few years can be expected.

[0005] The number of further possibilities is very large, but mayfrequently only be regarded as modifications of the above-describedprocesses, as the examples of organic solid-state laser diodes andorganic photodetectors demonstrate.

[0006] In some of these modern applications, development has alreadyprogressed a long way, but there is still, depending on the application,a tremendous need for technical improvements.

[0007] It can generally be assumed that both low molecular weightorganic semiconductors and polymeric organic semiconductors can besuitable for use in many of the abovementioned possible applications.Depending on the application, one of the two materials variants hasparticular advantages.

[0008] However, it may generally be stated that in the case ofapplications which require the use of undiluted or virtually undilutedsemiconductors, the appropriate coating methods for the low molecularweight or polymeric semiconductors can in principle be distinguished asfollows:

[0009] Low molecular weight semiconductors are then usually applied inthe appropriate layers by vacuum processes. Structuring is carried outby, for example, masking processes. Application by solution processes,e.g. various printing processes, doctor blade coating or spin coating,is generally unsuitable for undiluted low molecular weightsemiconductors, since it is frequently necessary to produce amorphouslayers, which in the case of these substances seldom succeeds fromsolution.

[0010] Polymeric semiconductors can usually be processed only fromsolution. Structuring can in this case be carried out by means of thecoating process used (e.g. various printing techniques) or by subsequenttreatment (e.g. photostructuring) or with the aid of typical photoresisttechniques (crosslinking, removal of regions that have not beencrosslinked, renewed coating, etc).

[0011] An important distinguishing feature when using low molecularweight or polymeric semiconductors is therefore the coating method.

[0012] Coating from solution is significantly easier to scale up. Whilevacuum coating is usually a batch process, a solution process can beoperated continuously when using suitable methods, which represents asignificant cost advantage and is advantageous for mass production.

[0013] It is therefore of great economic importance to providehigh-quality solutions of polymeric semiconductors which have a constantquality.

[0014] The use and preparation of such solutions has been widelydescribed, but up to now no importance has been attached to the actualpreparation of the actual solutions in a manner which can be scaled up.This could be due, in particular, to the fact that a reproducibleprocess has not been sought in most cases, but rather the research usewas first priority.

[0015] In the prior art which describes use of soluble conjugatedpolymers, the precise preparation of these solutions is not reported indetail:

[0016] EP 443861 describes a soluble PPV derivative (diheptyloxy-PPV)which can be applied from chloroform solution. The device parametersachieved in a PLED examined are totally unsatisfactory; nothing is saidabout the reproducibility of these results either.

[0017] Jpn. J. Appl. Phys. 1989, 28, L1433 analogously describes solublepolyfluorene derivatives. Here too, there is absolutely no informationon the preparation of stable solutions.

[0018] Analogous information may be found in all of the prior art.Although very good use properties have been reported for solutions ofpolymeric semiconductors, especially when used in PLEDs, there isvirtually no information at all on the reproducibility, availability andstability of the corresponding solutions.

[0019] As has been described above, it is therefore of great commercialinterest to provide high-quality solutions of polymeric semiconductorswhich have a constant quality. This is an object of the presentinvention.

[0020] To achieve good processibility, reproducibility and useproperties, the following parameters are important:

[0021] 1. Very constant concentration/viscosity ratio, which can beensured by a very constant molecular weight (very small batch-to-batchfluctuations).

[0022] 2 Highly pure solvent.

[0023] 3.Freedom from dust particles and particles in general.

[0024] 4.Availability in industrially relevant quantities.

[0025] 5. Stability of the solution over a relevant period of time.

[0026] Point 1 in particular is difficult to achieve in practice.Semiconducting polymers frequently have a high molecular weight (i.e.M_(w)>500 000, sometimes >1 000 000, M_(n) value>100 000, frequently>250000) and are obtained, for example, by polymerization(dehydrohalogenation polymerization in the case ofpoly-p-phenylenevinylenes [PPVs], cf., for example, EP-A-944663) orpolycondensation (e.g. Suzuki polymerization in the case ofpolyfluorenes [PFs], cf., for example, EP-A-1025142). Although theseprocesses can be readily controlled, reproduction of the molecularweight and polydispersity can generally not be readily achieved at willand variations in the range of at least ±5%, sometime about ±10% (cf.example 1) occur.

[0027] These fluctuations, which are small per se, then lead, however,to the following problems in the preparation of corresponding solutions:

[0028] If, for example, the concentration of the solution is fixed (e.g.5 g/l) and two polymers whose M_(w) values differ by about 10% (e.g. 1500 000 and 1 350 000) are used, two solutions which have asignificantly different viscosity (e.g. 25 mPa*s and 18 mPa*s @ 40 s⁻¹)are obtained (cf. example 1). The actually relatively small fluctuationsin the molecular weight thus lead to significant variations in theparameter which is of critical importance for the use properties ofpolymer solutions (viscosity or concentration/viscosity ratio).

[0029] This has drastic consequences for an industrial process: forsolutions which originate from a new polymer batch, the coatingparameters have to be completely reset, which at least greatly increasesthe costs and sometimes also prevents industrial use of thecorresponding solutions.

[0030] Point 3 is also a nontrivial problem in the case of polymericsemiconductors. As a result of the high molecular weight of thepolymers, filtration of the corresponding solutions is not easy. Thehigh molecular weight polymers sometimes form SUPRAMOLECULAR structures(chemical or physical aggregates) in solution, and these increase thesize of the already large polymer molecules still further. This leads tothe filters used very quickly becoming blocked, which is firstlyuneconomical and secondly makes the process either very slow(expensive).or sometimes virtually impossible.

[0031] It has surprisingly been found that solutions of polymericsemiconductors which have the abovementioned properties can be preparedsimply, efficiently and reproducibly.

[0032] The present invention accordingly provides a process forpreparing solutions comprising polymeric organic semiconductors, whichcomprises the steps:

[0033] A) dissolution of at least one polymeric organic semiconductor ina suitable solvent (STARTING SOLUTION),

[0034] B) after-treatment of the STARTING SOLUTION from step A)(SOLUTION),

[0035] C) filtration of the SOLUTION from step B) by means of dead-endfiltration and/or crossflow filtration and isolation of the filteredsolution comprising at least one polymeric organic semiconductor(FILTERED SOLUTION).

[0036] The preparation of the STARTING SOLUTION in step A) is carriedout by dissolving at least one polymeric organic semiconductor or amixture of a plurality of polymeric organic semiconductors (polymerblend), if desired in combination with one or more low molecular weightadditives (e.g. dopants to modify the color or conductivity), in thedesired solvent or solvent mixture. The STARTING SOLUTION can furthercomprise dispersion-like constituents. The preparation of the STARTINGSOLUTION in step A) is carried out under the action of shear forces, forexample by stirring or mixing, if desired with heating. The STARTINGSOLUTION is usually optically clear.

[0037] The after-treatment of the STARTING SOLUTION in step B) iscarried out by means of one or more mechanical after-treatment(s).Examples of suitable mechanical after-treatments are treatment withultrasound (e.g. ultrasonic bath, ultrasonic probe, flow-throughultrasonic apparatus), treatment with a fast-running, high-sheardispersing stirrer or mechanical treatment using a disintegrator. Thetreated STARTING SOLUTION is subsequently referred to as SOLUTION.

[0038] In step C), the SOLUTION from step B) is filtered. Suitablefiltration methods include both dead-end filtration and crossflowfiltration, which may also be combined with one another. Furtherfiltration methods can also be employed. These can, depending on therequirement profile to be met by the filtered solution, be employedbefore or after step C). In this way, higher throughputs can be achievedand blocking of the fine filter can be avoided or reduced. This gives aFILTERED SOLUTION.

[0039] If necessary, the FILTERED SOLUTION can be diluted to the desiredconcentration (+viscosity) by addition of filtered solvent. In this way,the concentration/viscosity ratio can be set in a targeted andreproducible fashion. The addition of filtered solvents or solventmixtures is advantageously carried out in clean rooms, for example inclean rooms of class 100, in particular class 10.

[0040] The solvents or solvent mixtures added have been freed ofparticles beforehand by filtration. The filters used have at least thesame pore size, preferably a smaller pore size, as/than those utilizedfor step C).

[0041] This process has the following advantages:

[0042] 1. The process can be scaled up and can thus be employed inindustry.

[0043] 2. The process leads to readily reproducible results.

[0044] 3. The process leads to solutions which, owing to their freedomfrom particles, are highly suitable for use in typical semiconductorapplications (cf. below).

[0045] 4. As a result of the reproducibility, the use of these solutionsis uncomplicated (when changing batches).

[0046] 5. The process leads to solutions which are stable for a longtime (cf. example 6).

[0047] In a preferred embodiment of the process of the invention, allprocess steps take place mostly under an inert atmosphere i.e. they arecarried out, for example, under nitrogen or argon.

[0048] Preference is also given to carrying out at least the filtrationand the optional final addition of solvent in a clean room environment.This helps to avoid subsequent introduction of dust particles.

[0049] It is then possible to use solutions of polymeric semiconductorswhich have been prepared in this way directly for the plannedapplication, i.e. to utilize them directly in an appropriate coatingprocess for the intended use.

[0050] Another possibility which is preferred from the point of view ofthe process sequence, is firstly to package the inventive solutionsproduced by the process of the invention, to store them if necessary, totransport them to another place and finally to use them only after sometime.

[0051] It is in this case useful to employ suitable containers which,firstly, preserve the freedom from dust achieved and, secondly, have noother effects on the solutions.

[0052] The present invention therefore also provides for dispensing thesolutions produced according to the invention into containers suitablefor clean-room conditions and then storing and transporting thesetightly closed. Dispensing itself is preferably carried out in cleanrooms of class 100, in particular class 10.

[0053] Such containers are known. Thus, for example, ATMI Packaging,Minneapolis, Minn. 55438 (formerly known as Now Technologies Inc.)markets bottles of various sizes which comprise a strong plastic ormetal bottle and have a totally inert insert of, for example, PTFE orPTFE/PFA. Further possibilities are, for example, glass or fused silicabottles which have been washed free of dust.

[0054] This dispensing and storage preferably continues to be carriedout under an inert gas atmosphere. It can be useful to seal theabovementioned plastic bottles into a further container and to fill thiscontainer with an inert gas.

[0055] The viscosity of the solutions of the invention is variable.However, certain coating techniques demand the use of particularviscosity ranges. Thus, an appropriate range for coating by ink jetprinting (IJP) is from about 4 to 25 mPa*s. However, a significantlyhigher viscosity, for example in the range from 20 to 500 mPa*s, can beadvantageous for other printing methods, e.g. gravure printing processesor screen printing.

[0056] The process of the invention can be employed for a large numberof polymeric semiconductors. For the purpose of the present invention,polymeric semiconductors are, in general terms, polymeric organic orpolymeric organometallic compounds which, in the form of a solid or acompact layer, display semiconducting properties, i.e. in which theenergy gap between conduction and valence band is in the range from 0.1to 4 eV.

[0057] For the purposes of the present description, polymeric organicsemiconductors are, in particular,

[0058] (i) the substituted poly-p-arylene-vinylenes (PAVs) which aresoluble in organic solvents and are disclosed in EP-A-0443861, WO94/20589, WO 98/27136, EP-A-1025183, WO 99/24526, DE-A-19953806 andEP-A-0964045,

[0059] (ii) the substituted polyfluorenes (PFs) which are soluble inorganic solvents and are disclosed in EP-A-0842208, WO 00/22027, WO00/22026, DE-A-19981010, WO 00/46321, WO 99/54385, WO 00/55927,

[0060] (iii) the substituted polyspirobifluorenes (PSFs) which aresoluble in organic solvents and are disclosed in EP-A-0707020, WO96/17036, WO 97/20877, WO 97/31048, WO 97/39045,

[0061] (iv) the substituted poly-para-phenylenes (PPPs) which aresoluble in organic solvents and are disclosed in WO 92/18552, WO95/07955, EP-A-0690086, EP-A-0699699,

[0062] (v) the substituted polythiophenes (PTs) which are soluble inorganic solvents and are disclosed in EP-A-1028136, WO 95/05937,

[0063] (vi) the polypyridines (PPys) which are soluble in organicsolvents and are disclosed in T. Yamamoto et al., J. Am. Chem. Soc.1994, 116, 4832,

[0064] (vii) the polypyrroles which are soluble in organic solvents andare disclosed in V. Gelling et al., Polym. Prepr. 2000, 41, 1770,

[0065] (viii) substituted, soluble copolymers comprising structuralunits from two or more of the classes (i) to (vii),

[0066] (ix) the conjugated polymers which are soluble in organicsolvents and are disclosed in Proc. of ICSM '98, Part I & II (in: Synth.Met. 1999, 101+102),

[0067] (x) substituted and unsubstituted polyvinylcarbazoles (PVKs) asdisclosed, for example, in R. C. Penwell et al., J. Polym. Sci.,Macromol. Rev. 1978, 13, 63-160, and

[0068] (xi) substituted and unsubstituted triarylamine polymers,preferably those disclosed in JP 2000-072722.

[0069] These polymeric organic semiconductors are hereby incorporated byreference into the disclosure of the present invention.

[0070] Polymeric organometallic semiconductors are described, forexample, in the unpublished patent application DE 10114477.6, e.g.organometallic complexes which have been incorporated into polymers bypolymerization.

[0071] The polymeric organic semiconductors used according to theinvention can also, as described above, be used in doped form or asblends with one another. For the present purposes, doped means that oneor more low molecular weight substances are mixed into the polymer;blends are mixtures of more than one polymer which do not necessarilyall have to display semiconducting properties.

[0072] Likewise, a large number of different solvents are in principlepossible for the process of the invention. However, prerequisites forviable industrial use are the following boundary conditions:

[0073] 1. The solvent or solvent mixture has to be available or at leastaccessible in sufficient amounts.

[0074] 2. The solvent or solvent mixture has to be available in a purityappropriate for the application or at least has to be able to be broughtto this purity by means of industrially usable processes.

[0075] 3. The solvent or solvent mixture has to have physical propertiessuitable for the application (e.g. melting point, boiling point, vaporpressure, viscosity, environmental acceptability, toxicity).

[0076] There are many examples of solvents which can be used: aromaticsolvents such as substituted benzenes (e.g. toluene, anisole, xylenes),heteroaromatics, e.g. (pyridine and simple derivatives), ethers (e.g.dioxane) and further organic solvents are frequently used.

[0077] Solvents specifically for solutions of polymeric semiconductorshave also been described in various patent applications.

[0078] EP-A-1083775 proposes, in particular, high-boiling aromaticsolvents which have a preferred boiling point above 200° C., and arebenzene derivatives which possess at least three carbon atoms in theside chain or chains. In the patent application mentioned, solvents suchas tetralin, cyclohexylbenzene, dodecylbenzene and the like arementioned as preferred.

[0079] EP-A-1103590 analogously reports solvents in general having avapor pressure (at the temperature of the coating process) of less than500 Pa (5 mbar), preferably less than 250 Pa (2.5 mbar) and once againdescribes solvents or solvent mixtures of mainly (highly) substitutedaromatics.

[0080] On the other hand, the unpublished patent application DE10111633.0 mentions solvent mixtures consisting of at least twodifferent solvents of which one boils in the range from 140 to 200° C.In general, solvent mixtures comprising mainly organic solvents such asxylenes, substituted xylenes, anisole, substituted anisoles,benzonitrile, substituted benzonitriles or heterocycles such as lutidineor morpholine are likewise described here.

[0081] These can be, for example, mixtures of solvents of the group Adescribed below with solvents of group B.

[0082] Group A:

[0083] o-xylene, 2,6-lutidine, 2-fluoro-m-xylene, 3-fluoro-o-xylene,2-chlorobenzo-trifluoride, dimethylformamide, 2-chloro-6-fluorotoluene,2-fluoroanisole, anisole, 2,3-dimethylpyrazine, 4-fluoroanisole,3-fluoroanisole, 3-trifluoromethylanisole, 2-methylanisole, phenetol,4-methylanisole, 3-methylanisole, 4-fluoro-3-methyl-anisole,2-fluorobenzonitrile, 4-fluoroveratrole, 2,6-dimethylanisole,3-fluoro-benzonitrile, 2,5-dimethylanisole, 2,4-dimethylanisole,benzonitrile, 3,5-dimethylanisole, N,N-dimethylaniline,1-fluoro-3,5-dimethoxybenzene or N-methylpyrrolidinone.

[0084] Group B:

[0085] 3-fluorobenzotrifluoride, benzotrifluoride, dioxane,trifluoromethoxybenzene, 4-fluorobenzotrifluoride, 3-fluoropyridine,toluene, 2-fluorotoluene, 2-fluoro-benzotrifluoride, 3-fluorotoluene,pyridine, 4-fluorotoluene, 2,5-difluorotoluene,1-chloro-2,4-difluorobenzene, 2-fluoropyridine, 3-chlorofluorobenzene,1-chloro-2,5-difluorobenzene, 4-chlorofluorobenzene, chlorobenzene,2-chlorofluoro-benzene, p-xylene or m-xylene.

[0086] The likewise unpublished German patent application DE 10135640.4discloses the use of solvents analogous to those mentioned above and,apart from the polymeric semiconductors and the solvents, furtheradditives, preferably siloxane-containing additives.

[0087] To carry out the process of the invention, polymericsemiconductors (one or more), e.g. ones selected from theabove-described classes, are dissolved in solvents, e.g. solventsselected from among the above-described examples.

[0088] For this purpose, the amount of polymer necessary for the desiredconcentration, if desired somewhat more, is firstly added to therequired amount of solvent.

[0089] The solutions to be prepared should contain from 0.01 to 20% byweight, preferably from 0.1 to 15% by weight, particularly preferablyfrom 0.25 to 10% by weight, very particularly preferably from 0.25 to 5%by weight, of the polymeric semiconductors. A mixture/blend of more thanone polymeric semiconductor can also be used according to the invention.

[0090] The solution itself is prepared in a container appropriate forthe desired volume. Thus, small amounts (up to about 500 ml) can, forexample, be made up without problems in suitable glass or plasticbottles.

[0091] Moderate amounts (up to about 20 l) can, for example, be made upin standard laboratory glass or fused silica apparatus.

[0092] Larger amounts (from 20 to >1 000 l) have to be made up insuitable plants and suitable rooms because of the hazard potential oforganic solvents. These can be, for example, normal vessels for chemicalsyntheses. However, owing to the high purity requirements, these vesselshave to be specially cleaned and have particular internal surfaces. Forthe production of thin films in particular, contamination with metalparticles and ionic impurities should generally be avoided. Preferenceis therefore given in principle to very smooth and abrasion-resistantcontainer surfaces. It can also be advantageous for no metallic surfacesto come into contact with the solutions.

[0093] As indicated above, it is frequently advantageous to carry outthe process under an inert atmosphere. Particularly in the case ofrelatively large quantities, this generally also provides the necessaryexplosion protection, since very many organic solvents form explosivegas mixtures with air and hazards are therefore difficult to eliminatewhen working in an ambient atmosphere.

[0094] According to the invention, a STARTING SOLUTION is prepared bystirring or mixing and heating.

[0095] Stirring or mixing can be carried out by means of a large numberof different methods:

[0096] It is possible to use, for example, standard stirring apparatuses(e.g. magnetic stirrers, precision glass stirrers, industrial agitators)or pumped circulation mixers (mixing by frequent pumping through anangled tube system). However, mixing can also, for example, be achievedby shaking using an appropriate apparatus. As in the case of theselection of the vessel, care has to be taken to ensure that thesolution is not contaminated by the mixing process. Further potentialmixing methods may be found, for example, in Ullmann's Encyclopedia ofIndustrial Chemistry, 6^(th) Edition, WILEY-VCH, 2001.

[0097] Heating can be carried out within a wide temperature range.

[0098] This temperature range is usually from room temperature (20° C.)and the boiling point of the solvent (or mixture). It may also beadvantageous to work under superatmospheric/subatmospheric pressure andthus extend the range of usable temperatures.

[0099] However, a working range from 20 to 100° C., preferably from 40to 80° C., has been found to be appropriate in practice.

[0100] The appropriate period of time depends on a variety of factors,e.g. the desired concentration, the form of the polymer solid, themolecular weight of the polymer, the solvent, the actual temperatureselected, the type and power of the stirrer or mixer, the ratio ofvessel size to mixture power and further circumstances. However, theperiod of time will usually be in the range from 0.5 to 100 hours,preferably from 2 to 40 hours, particularly preferably from 2 to 25hours.

[0101] The STARTING SOLUTION obtained in this way is then subjected tomechanical after-treatment. This treatment, which is described in moredetail below, is carried out for, inter alia, the following reasons:

[0102] STARTING SOLUTIONS of polymeric semiconductors frequently containnot inconsiderable amounts of aggregates. These firstly alter theproperties of the semiconductors in the film (e.g. conductivity, color)and secondly, as described above, they make filtration of the respectiveSTARTING SOLUTIONS more difficult since they very easily block the poresand/or channels of the filters used. These aggregates can be completelybroken up by the mechanical after-treatment, or their proportion can atleast be reduced significantly (cf. example 2).

[0103] An important aspect is that the molecular weight of the polymerscan be reduced by targeted use of these mechanical processes withouthaving a significant influence on the performance of the material in theapplication. This can be used very advantageously to compensate for theabovementioned batch fluctuations due to the synthesis. It is in thisway also possible to achieve a very reproducible concentration/viscosityratio (cf. example 1).

[0104] Furthermore, the processes for mechanical after-treatment canactually be employed to produce a targeted, relatively large decrease inthe molecular weight when, for instance, particular applications or, forexample, coating processes impose upper limits on the molecular weight.Such upper limits have been described, for example, for printingprocesses such as ink jet printing (cf. US-A-2001/0003602). For furtherdetails, reference may also be made to example 3.

[0105] The mechanical treatment can, inter alia, be carried out asdescribed below. It may be pointed out that not all methods are equallysuitable for every batch size. Thus, for example, the use of standardultrasonic baths for solutions in the 1000 l range is uneconomical,while the use of appropriate flow-through apparatuses can be technicallyimpracticable for small quantities (e.g. <5-20 l) because of the highdead volumes. Nevertheless, with appropriate adaptation, various methodscan lead to a similar result.

[0106] 1. One simple possibility is the use of commercial ultrasonicbaths. These are obtainable in various sizes and various power ratings.Important parameters here are volume, ultrasonic power and ultrasonicfrequency. The mechanical treatment is carried out by placing theSTARTING SOLUTION in a suitable container (e.g. glass vessel, plasticbottle) in the ultrasonic bath and sonicating it for a particular time(which depends essentially on the degree of aggregation or the intendedreduction in molecular weight). It can also be found to be advantageousto keep the temperature constant during sonication or keep it below aparticular maximum temperature. It can likewise be useful to providegood mixing during sonication so that the ultrasonic power introducedacts homogeneously on the contents of the vessel. Commercially availableultrasonic apparatuses which are suitable for use in this way are, forexample, BANDELIN USR 170D (17 l, 2×450 W), BANDELIN RM 75UH (87 l,2×2000 W), BANDELIN RM 210UH (243 l, 2×4000 W), BANDELIN RK 514BH (19 l,2×450 W); BANDELIN RK 1050CH (90 l, 2×1200 W), BRANSON 8510 DTH (20 l,320 W), ELMA TS 820H (18 l, 2×600 W) and further products from theabovementioned or other manufacturers.

[0107] 2. One or more ultrasonic probes can also be used in an analogousfashion for carrying out the mechanical treatment. In this case, theseare generally introduced directly into the STARTING SOLUTION. What hasbeen said under 1 applies analogously here: temperature control andmixing can be advantageous. The time is once again determined mainly bythe consistency of the SOLUTION to be achieved. Suitable commerciallyavailable ultrasonic probes are, for example, BANDELIN SONOPLUS 2600(600 W, 20 kHz) and BRANSON SONIFIER 450 DIGI (½″) (400 W, 20 kHz) andfurther products from the abovementioned or other manufacturers. Adisadvantage which could be very difficult to avoid when using theseprobes could be the abraded material (titanium particles) produced atthe tips of these probes. However, this abraded material can becompletely removed again by subsequent filtration.

[0108] 3. A further possible way of using ultrasound is provided byvarious flow-through apparatuses. Thus, there are simple flow-throughcells through which the solutions can be pumped and in which, forexample, ultrasonic probes are installed. Suitable flow-through cellsare obtainable, for example, from BRANSON. Furthermore, there are alsoflow-through tubes which function in the manner of a tubular ultrasonicbath; an example is the PENTAGONAL system from BRANSON: PENTAGONALtubular sonicator LP 6.80-35+HF generator B-8540 LP-35 (40 kHz, 3 kW).The use of such apparatuses is firstly advantageous with a view toscaling up such a process, and, secondly, the mechanical effect cansometimes be regulated better, e.g. by selection of the flow rate, thanwhen using simple ultrasonic baths or ultrasonic probes. Otherwise, theremarks made under 1. and 2. apply.

[0109] 4. A further possibility is the use of high-shear dispersingstirrers, dispersers or high-speed stirrers. These are available invarious designs and power ratings. In particular, they can also be usedadvantageously for larger volumes (>500 l), since these stirrers areavailable in industrial sizes. In a manner analogous to mechanicaltreatment with ultrasound, temperature control during the actualdispersing process can also be advantageous here. Suitable stirrers are,for example, HEIDOLPH DIAX 900 (up to 7.5 1, up to 5000 mPa*s, 495 W,8000-26 000 min⁻¹), KINEMATIC POLYTRON series (up to 301, up to 1600 W,up to 30 000 min⁻¹), IKA ULTRATURRAX series (up to 50 l, up to 1100 W,up to 25 000 min⁻¹), MICCRA D series (up to 50 l, up to 1300 W, up to 39000 min⁻¹), various models of YSTRAL, EKATO stirrer (up to 1000 l, 5.5kW, 95-950 min⁻¹) and further products from the abovementioned or othermanufacturers.

[0110] 5. Another possible way of carrying out the mechanical treatmentis the use of disintegrators. These usually operate according to thefollowing principle: the STARTING SOLUTION is pushed with the aid of apump through a microchamber at high pressure (high velocity). As aresult of the specific geometry of these chambers, tremendous shearforces are applied to the solution. This achieves ultrasound-likeeffects (breaking up of aggregates, reduction in the molecular weight).The entire process can be operated with circulation (possibly withcontinuous further addition and discharge) or be used as a step in alonger process. As in the case of the various ultrasonic methods andwith dispersion, temperature control and potential further mixing can befound to be advantageous here. This method in particular is very usefulfrom the point of view of scale-up. Suitable apparatuses are suppliedby, for example, MicroFluidics (e.g. MICRO FLUIDIZER PROZESSOR M-110 EH,equipped with 100 μm or 200 μm chamber; the chamber is obtainable, forexample, in ceramic or diamond).

[0111] The following then applies to the practical implementation of allthese mechanical treatment methods described here and also furtheranalogous methods which have not been explicitly listed here:

[0112] To obtain a desired concentration/viscosity ratio, a suitableSTARTING SOLUTION is prepared first and this is examined to determinethe parameters mentioned (concentration, viscosity) (cf. examples). Thevalues of these parameters for the STARTING SOLUTION should preferablybe above those desired in the end, since thickening of the solutions isnot very practicable industrially and is disadvantageous with regard toparticle contamination and, furthermore, when the concentration iscorrect but the viscosity is too low, there is no way, with theexception of the addition of thickeners, of increasing the viscosity.The addition of such thickeners would firstly have to be checked forcompatibility in each application, which is undesirable in an industrialcontext.

[0113] This STARTING SOLUTION is then subjected to the chosen mechanicalafter-treatment process and the change in the concentration/viscosityratio is monitored, either ON-LINE or by ongoing sampling. When thedesired value has been achieved (or the measured value is at least closeto this) mechanical treatment is stopped. As an alternative, it is alsopossible, for example, to monitor the molecular weight via GPC or theparticle size via light scattering methods.

[0114] If the abovementioned processes are carried out a plurality oftimes for a particular polymer, it is generally possible to dispensewith continual monitoring since the treatment time found in the firstrun is usually very reproducible (cf. example 4).

[0115] The SOLUTION obtained in this way is then filtered. In thisfiltration, attention has to be paid to a variety of technical boundaryconditions:

[0116] The filtration should be economical, i.e. the filtration rates(e.g., ml or l of SOLUTION/min and filter size) should be in apracticable range. This cannot be limited in terms of specific figures,but will certainly be made understandable to a person skilled in the artby the following: if, for example, 50 l of SOLUTION are to be filtered,the filter elements should be able to be chosen so that the loss ofvolumes (i.e., for example, dead volume of the filter element, solutionfor flushing the filter, etc.) add up to not more than 5 l, preferablyless than 2 l (i.e. not more than 10%, preferably less than 4%).Furthermore, the filtration should be able to be carried out within anacceptable time interval (for example within a working

[0117] The filter elements used should be commercially available.

[0118] The filter elements used and the associated holders should reactvery little, preferably not at all, with the SOLUTIONS. This requirementmay seem to be trivial, but in practice represents a nontrivial problem.Thus, very many filter elements are made up of polymeric materials andcontain adhesives and sealing rings and much more. However, the entirefilter element has to be virtually totally resistant to the SOLUTIONused. This is usually only the case for elements which consist entirelyof fully fluorinated polymers (e.g. PTFE) or exclusively inorganicmaterials. However, it is frequently possible to make elements which arenot totally stable usable by means of an appropriate pretreatment (cf.example 5).

[0119] The degree of filtration (i.e. the size of the particles whichare filtered out [e.g. with a probability of >99.9%]) has to bepracticable for the application while still enabling the abovementionedpoints (e.g. economic viability) to be met.

[0120] It can be useful to circulate the SOLUTION a number of timesthrough the same filter element until, for example, a particle countingmethod or another method of quality control demonstrates the quality ofthe filtered SOLUTION.

[0121] The filtration per se can in principle be carried out in avariety of apparatuses. Since, however, particular boundary conditions(e.g. preferred treatment of the SOLUTION under an inert atmosphere,avoidance of dust contamination of the filtered SOLUTION) are to beadhered to, the following is appropriate:

[0122] It is advisable to use the complete unit (comprising containerfor SOLUTION, pump system, filter element, container for collection ofthe filtered SOLUTION including pressure equilibration, any pipes andpump circulation systems) as a closed system in order to make itpossible for inert conditions to be obtained efficiently.

[0123] It is also advisable to set up the container for the filteredSOLUTION (and any blending or dispensing apparatuses) in a dust-freeenvironment (e.g. clean room).

[0124] In the choice of equipment (e.g. pumps, pipes, etc.), attentionshould be paid, at least in the case of the parts which come intocontact with SOLUTION, to their inertness toward the solvents used orthe SOLUTIONS.

[0125] An apparatus which is in principle suitable for preparing thesolutions of the invention can then be as follows:

[0126] The container in which the SOLUTION is present is connected via apipe system to a chemically inert pump. This is in turn connected to an(exchangeable) filter element which finally opens via a further pipesystem into a collection vessel. The collection vessel is eitherprovided with sampling facilities or contains probes by means of whichthe parameters viscosity and concentration can be determined directlyon-line. The collection vessel is also possibly connected with ablending unit and a dispensing unit. Dedicated filtration systems canalso be installed in each of these.

[0127] The entire filtration procedure is carried out at a low admissionpressure, preferably in the range from 10 mbar to 3 bar.

[0128] It is advantageous for the entire apparatus to be able to beoperated under an inert atmosphere.

[0129] It is also industrially advantageous for the individual regionsof the apparatus to be able to be cleaned independently of one another(e.g. by multiple pumping-through of pure solvents).

[0130] The actual filtration can be carried out using, taking intoaccount the abovementioned criteria, a number of filter elements:

[0131] Examples of filter elements which can be used are deep bedfilters, membrane filters and combi filters; various filter types (whichcan readily be scaled up) are supplied, for example, by the companiesPALL, MILLIPORE, SCHLEICHER & SCHÜLL, SARTORIUS, ULTRAFILTER and furtherspecialist companies.

[0132] Usable filter elements can comprise, for example, polypropylene(PP), cellulose, PTFE, PTFE-PFA and similar plastics.

[0133] An example of a deep bed filter series which can be used is PALLPROFILE II. This type of filter is obtainable in lengths from 1″ to 40″(diameter, for example, 7 cm), in degrees of filtration of from >5 μm to<0.3 μm and with various sealing and connection systems. The filtermaterial is PP, which is virtually inert toward standard solvents afterbrief initial rinsing.

[0134] An example of a membrane filter which can be used is MILLIPOREFLUOROGARD AT or ATX. This filter type is available in sizes of from 4″to 30″, in degrees of filtration of from 1 μm to 0.05 μm and withvarious sealing and connection systems. The filter material is PTFE andPFA and has very good stability toward customary solvents.

[0135] As has been stated above, the actual filtration is preferablycarried out in a plant suitable for this purpose. Once again, thesolution can flow through the actual filter element in various ways. Thecrossflow process, i.e. the solution moves virtually parallel to theplane of the filter, is one possibility. However, dead-end filtration,i.e. the solution moves virtually perpendicular to the plane of thefilter, is also possible. In addition, further filtration methods can beused in the process of the invention.

[0136] After the filtration has been carried out in the manner describedor in a similar way, the actual process of the invention is complete.

[0137] As indicated above, the concentration and viscosity willgenerally be determined again before use of the solution prepared, sincethese can easily change during filtration, e.g. as a result ofindividual polymer particles being held back or due to evaporation of alittle solvent. As described, the final concentration and viscosity canthen be set by addition of a little filtered solvent.

[0138] The resulting filtered solution of polymeric semiconductors canthen either be used directly or be packaged, stored, transported (seeabove) and only used later in another place.

[0139] Since the solutions of polymeric semiconductors producedaccording to the invention are distinguished from the prior art by, inparticular, their quality, reproducibility, reliability and storagestability, they are accordingly additional subject matter of the presentinvention. The invention thus provides solutions of polymericsemiconductors which have been obtained by the above-described process.

[0140] Despite the filtration which takes place in the process of theinvention, preference is given to allowing the solutions producedaccording to the invention to run through a filter once againimmediately before use. This filter can have a (significantly) largerpore size. It serves as a “point-of-use” filter which eliminates dustwhich has “sneaked in” after the filtration. A further aspect of thepresent invention therefore provides for the solutions of the inventionto be filtered again directly at the place of use.

[0141] As described above, the solutions of the invention can then beused for producing coatings comprising polymeric semiconductors. Thesehave the advantage, especially in comparison with the prior art, ofbetter reproducibility, which is of critical importance for industrialuse. The reliability is also generally higher, since the process leadsto solutions which have a very low particle content.

[0142] The invention therefore also provides for the use of thesolutions of the invention for producing layers of polymericsemiconductors.

[0143] These layers can be produced with the aid of the solutions of theinvention so as to either cover the full area or be structured. Variousindustrial coating processes can be used for this purpose. For full-areacoating, it is possible to use, for example, processes such as doctorblade coating, spin coating, meniscus coating or various printingprocesses. Suitable methods for resolved, structured coating are, inparticular, various printing processes, e.g. transfer printing, ink jetprinting, offset printing, screen printing, to name only a few customaryexamples.

[0144] The invention therefore also provides for the use of thesolutions of the invention for producing coatings using coatingprocesses such as doctor blade coating, spin coating, transfer printing,ink jet printing, offset printing or screen printing.

[0145] As has likewise been mentioned above, these layers can be used ina variety of applications.

[0146] Examples which may be mentioned are the following electroniccomponents: polymeric organic light-emitting diodes (PLEDs), organicintegrated circuits (O-ICs), organic field effect transistors (OFETs),organic thin film transistors (OTFTs), organic solar cells (O-SCs) andorganic laser diodes (O-lasers).

[0147] The invention therefore also provides for the use of thesolutions of the invention for producing layers of the invention for usein polymeric organic light-emitting diodes (PLEDs), organic integratedcircuits (O-ICs), organic field-effect transistors (OFETs), organic thinfilm transistors (OTFTs), organic solar cells (O-SCs) or organic laserdiodes (O-lasers).

[0148] The present invention is illustrated in more detail by thefollowing examples without being restricted thereto. A person skilled inthe art can, on the basis of the description and the examples given,prepare further solutions according to the invention and use them forproducing layers without any further inventive step.

EXAMPLE 1 Reproducibility of Polymer Batches

[0149] 1.1 Batches of Polymer Solids:

[0150] 7 batches of a yellow-emitting PPV derivative (structureanalogous to polymer P6 in EP-A-1029019) were produced in an industrialapparatus (360 1 enameled VA vessel, stirrer, reflux condenser, variousmetering devices, temperature control, nitrogen regulation). Afterappropriate work-up and purification, the PURE polymers were obtainedand were then available for preparing solutions. These polymers had theproperties shown in the following table: TABLE 1 Data for the polymerbatches P-1 to P-7. Batch P-1 P-2 P-3 P-4 P-5 P-6 P-7 Viscosity¹⁾ ˜25˜22 ˜18 ˜26 ˜21 25.3 10.5 at 40 s⁻¹ [mPa * s] GPC²⁾: Mw/1000 1495 14401355 1615 1550 1510 1250 Mn/1000 405 420 400 380 420 420 300 EL³⁾ (max.eff.; 12.3 Cd/A 11.8 Cd/A 11.9 Cd/A 12.4 Cd/A 11.5 Cd/A 11.1 Cd/A 11.8Cd/A U at 100 Cd/m²) 3.2 V 3.2 V 3.6 V 3.2 V 3.7 V 3.7 V 3.7 V ELstandard 10.1 Cd/A 10.2 Cd/A 10.4 Cd/A 10.8 Cd/A  9.9 Cd/A  9.9 Cd/A10.7 Cd/A 3.7 V 3.9 V 3.5 V 4.0 V 3.6 V 3.6 V 3.7 V

[0151] 1.2 Polymer Solution Batches:

[0152] Polymer solutions were then prepared using the abovementionedbatches. The aim was to prepare solutions suitable for spin coating. Theprescribed specification was as follows: Solvent: Toluene (MERCK, ARgrade #108325) Concentration (w/v): 4.25 ± 0.25 g/l Viscosity (at 40s⁻¹) 10.0 ± 1.2 mPa * s Viscosity (at 500 s⁻¹)  9.0 ± 1.0 mPa * s

[0153] The solutions were then prepared as follows:

[0154] A 6 l glass flask (with reflux condenser, nitrogen blanketing,precision glass stirrer with magnetic coupling, internal thermometer)was charged with 5 l of toluene and purged with nitrogen for 30 minutes;25 g (5 g/l) of the respective polymer were subsequently introduced andthe mixture was stirred at an internal temperature of about 65° C. for24 hours. The STARTING SOLUTION prepared in this way was treatedmechanically for a particular time (cf. table) in a BANDELIN RK 514BHultrasonic bath at an internal temperature of about 10° C., subsequentlyfiltered in a clean room (CR class 100) through a PALL PROFILE II filter(0.3 μm, 1″, flow rate about 15 ml/min) and subsequently admixed with asmall amount of toluene (prefiltered). The solutions obtained in thisway were packaged and subsequently used for producing coatings by spincoating. Highly efficient polymeric LEDs were able to be produced fromthem. The efficiencies and voltages corresponded, within the limits ofmeasurement accuracy, to the values shown in table 1.

[0155] Further data on the solutions are shown in the following table:TABLE 2 Solutions of the polymers P-1 to P-7. Solution of P-1³⁾ P-2⁴⁾P-3 P-4³⁾ P-5³⁾ P-6 P-7 Time of application of 102 31 20 82 67 35 10ultrasound [min] Concentration¹⁾ [g/l] 4.49 4.42 4.45 4.24 4.33 4.464.63 Viscosity¹⁾ 9.82 9.97 10.1 10.49 10.38 10.40 9.21 at 40 s⁻¹ [ mPa *s] Viscosity¹⁾ 8.95 8.85 9.15 9.55 8.83 9.38 8.56 at 500 s⁻¹ [ mPa * s]GPC²⁾: M_(w)/1000 1210 1230 1240 1250 1240 1230 1180 M_(n)/1000 380 390400 380 390 400 300

[0156] Comparison of the data in table 1 and table 2 enables thefollowing conclusions to be drawn:

[0157] Use of the process of the invention makes it possible, albeit forrelatively different polymer batches (cf., for example, P-3 with P-4),to produce uniform solutions having a virtually constant quality (note:the accuracy of, for example, the concentration determination is in therange of ±0.1 g/l, and the reproducibility of viscosity data is likewiseat a maximum in the range of ±0.3 mPa*s).

[0158] The increase in uniformity is achieved, in particular by theM_(w) being reduced. This is initially presumably due mainly todestruction of aggregates (cf. example 2).

[0159] Without use of a mechanical treatment process, the variation inthe viscosity (cf. data in table 1) would be significantly greater.

[0160] Only in the case of the outlier batch P-7 was it not possible tomeet the tight specification (excessively high concentration); however,this batch, too, made it possible to come very close to the desiredrange.

EXAMPLE 2 Aggregates in Solutions of Polymeric Semiconductors

[0161] As indicated in the description, untreated solutions of polymericsemiconductors frequently contain a high proportion of aggregates. Thisproportion is significantly reduced by the mechanical treatment (asindicated, for example, in the description or in example 1).

[0162] These aggregates can be detected by means of various tests. Twoexamination methods are used below.

[0163] 2.1 Filterability of Solutions of Polymeric Semiconductors:

[0164] As stated above, untreated solutions of polymeric semiconductorscan lead to blocking of filter elements. In this example, a solution ofpolymer P-1 (cf. example 1) was used and the filterability was observedafter different treatment times. The results are shown in table 3.

[0165] 2.2 Optical Examination of Solutions of Polymeric Semiconductors:

[0166] Particle sizes in solutions can in principle be measured byvarious scattering methods. In the case of the generally stronglycolored solutions of polymeric semiconductors, the method of“noninvasive backscattering” (NIBS) has been found to be useful. Acorresponding particle counting apparatus is marketed by ALV. Althoughthis method does not, in our experience, allow absolute particle sizesto be determined, information on tendencies can readily be obtained. Theresults are likewise shown in table 3.

[0167] For the tests described under 2.1 and 2.2, a solution of polymerP-1 was prepared (in total 10 l; preparation analogous to example 1).The appropriate tests were then carried out without use of ultrasound,after application of ultrasound for 50 minutes and after application ofultrasound for 100 minutes. As filter element, a 1″ cartridge asdescribed in example 1 was used. TABLE 3 Sonication of polymer P-1.NIBS²⁾ Area of Area of peak Filtration polymer Area of due to US timeFilter becomes rate peak middle aggregates [min] blocked after¹⁾[ml/min] [%] peak [%] [%]  0 100 ml   3 → 0.2  2  6 92  50 ˜1000 ml 15 →1  14 20 66 100 >5 l constant: 15 35 20 45

[0168] The results indicate the following:

[0169] The untreated solutions were difficult to filter.

[0170] The number of aggregates was significantly reduced by mechanicaltreatment.

EXAMPLE 3 Active Reduction in Molecular Weight by Mechanical Treatment

[0171] As indicated in the description, some coating processes may makeit necessary to set concentration/viscosity ratios which cannot beachieved directly by means of polymers prepared by standard methods.Furthermore, particular uses (e.g. ink jet printing) can prescribe orsuggest certain upper limits to the molecular weights because ofrheological requirements.

[0172] Solutions of polymeric semiconductors were then to be preparedfor use in ink jet printing processes.

[0173] The solutions should have the following properties: Solvent:Anisole/o-xylene (1:1) Concentration (w/v):   14 ± 0.5 g/l Viscosity (at40 s⁻¹) 10.0 ± 0.6 mPa * s or 15-18 mPa * s Viscosity (at 500 s⁻¹) 10.0± 0.6 mPa * s or 15-18 mPa * s

[0174] Both a solution of a yellow-emitting PPV derivative and of ablue-emitting polyspirofluorene derivative were then to be prepared.

[0175] The polymer P-7 (cf. example 1) and the polymer P-8(blue-emitting polyspiro derivative, structure analogous to polymer P12in DE 10114477.6) were used.

[0176] The preparation of the solution was initially carried out in amanner analogous to example 1, but significantly longer ultrasonicationtimes were used.

[0177] The effect of sonication was monitored via measurement of theviscosity. At the end, a GPC analysis of the solutions was also carriedout. The results are summarized in the following tables: TABLE 4Sonication of polymer P-7. Ultrasonication mPa * s mPa * s time [h]¹⁾ at40 s⁻¹ at 500 s⁻¹  0 327 133 12 194 110 22 120 88 30 82 68 41 33 30 5220 18.5 59 17 17 GPC values²⁾ M_(w)/1000 M_(n)/1000  0 h US 1180 300 59h US 350 150

[0178] TABLE 5 Sonication of polymer P-8. Ultrasonication mPa * s mPa *s time [h]¹⁾ at 40 s⁻¹ at 500 s⁻¹  0 115 57  8 15 15 14 11.8 11.8 1711.0 11.0 22 9.9 9.9 GPC values²⁾ M_(w)/1000 M_(n)/1000  0 h US 1220 26022 h US 560 260

[0179] Structured PLEDs could be produced by ink jet printing from thesolutions prepared in this way. The solutions were printed, for example,using a Spectra Galaxy 256/80 or 256/20 printing head.

[0180] The following can be seen from the results:

[0181] The process of the invention also makes it possible to obtainsolutions of polymeric semiconductors which have unusualconcentration/viscosity ratios.

[0182] The mechanical treatment makes a controlled reduction in themolecular weight possible.

[0183] Solutions which have been treated mechanically for a relativelylong time behave as ideal NEWTON solutions (i.e. the viscosity remainsconstant regardless of the shear applied).

EXAMPLE 4 Reproducibility of the Process of the Invention

[0184] As emphasized a number of times in the description, thereproducibility is frequently of critical importance for industrialprocesses. In the present context, this means, firstly, the preparationof a very constant solution quality and, secondly, a very high constancyof the production parameters.

[0185] This is demonstrated by the following experiment:

[0186] As indicated in example 1 (1.2, table 2) for a number ofpolymers, the data reported there are the means of a plurality ofsolution preparations. This is described in more detail below for thepolymer P-4:

[0187] A total of 9 solutions (prepared in a manner analogous toexample 1) were employed for this purpose. The amounts of solutionvaried from 5 to 15 l.

[0188] The values achieved are shown in the following table: TABLE 6Reproducibility of constant solution quality for polymer P-4.Viscosity²⁾ EL data³⁾ Initial US Final at at max. U [V] Ref. Solutionconc. time conc. 40 s⁻¹ 500 s⁻¹ eff. at 100 eff. Ref. U number [g/l]¹⁾[h] [g/l]¹⁾ [mPas] [mPas] [Cd/A] Cd/m² Cd/A] [V] P-4-01 4.96 0.75 4.329.78 9.52 11.8 3.2 10.5 3.4 P-4-02 4.98 1 4.26 10.80 9.34 10.4 3.2 9.73.5 P-4-03 5.04 1.6 4.26 10.50 8.97 10.6 3.4 9.7 3.7 P-4-04 4.96 1.54.19 10.20 9.45 11.8 3.2 10.1 3.7 P-4-05 5.01 1.5 4.23 10.60 9.82 10.93.2 10.7 3.4 P-4-06 4.97 1.5 4.21 10.20 9.71 11.3 3.4 9.7 3.9 P-4-074.98 1.5 4.25 10.60 10.00 11.1 3.4 9.8 3.9 P-4-08 5.03 1.5 4.26 10.609.93 12.3 3.2 9.8 3.9 P-4-09 5.09 1.5 4.21 11.14 9.23 10.78 3.2 9.673.65 Means 5.00 1.37 4.24 10.49 9.55 11.22 3.27 9.96 3.67

EXAMPLE 5 Stability of Filter Elements Used

[0189] As stated in the description, it is important that no impuritiesare introduced into the solutions of polymeric semiconductors by thevarious operations. In the process steps “dissolution”, “mechanicaltreatment” and “dilution & packaging & storage”, this can generally beachieved without problems by appropriate selection of media (e.g.electropolished stainless steel, glass or fused silica vessels, orenameled vessels, or PTFE/PFA-coated apparatuses). In the case offiltration, the situation is somewhat different, since there are atpresent only a limited number of solvent-stable commercial filterelements. Apart from some elements (very expensive all-PTFE/PFAelements), recourse therefore frequently has to be made to elementswhich are not totally stable. That this is nevertheless possible undersuitable conditions, is demonstrated by this example:

[0190] The filter type PALL PROFILE II which is frequently used in theabove examples consists entirely of polypropylene (PP). Seals made ofFEP-sheathed VITON can be obtained. The seals thus have a goodresistance to solvents. However, PP is not totally stable.

[0191] However, the following has been discovered: on contact withsolvents, the filter elements release a certain amount of material.However, this does not alter the filter consistency. In addition, therelease of material is strongly time-dependent. The material releasedwas able to be identified unambiguously as PP having a relatively lowmolecular weight (¹H NMR, GPC, comparison with reference samples). Thetests were carried out as follows:

[0192] Five solutions were produced in parallel by placing filtermaterial (in each case 100 g) in solvent (in this case toluene) at roomtemperature (25° C.) for a particular time (see table). After the timehad expired, the solvent was evaporated, the amount of extract wasdetermined and the extract was in each case analyzed by NMR and GPC.Furthermore, some of the filter samples were additionally examined forchanges by electron microscopy.

[0193] The results are summarized in the following table: TABLE 7Extraction tests on PALL PROFILE II filter elements; here parts of 10″,0.5 μm cartridges. Amount of Identification Filter after Timeextract[mg] of extract extraction (EM)¹⁾ 10 min  80 mg PP, M_(w) ˜5000no change 30 min 180 mg PP, M_(w) ˜5000 no change  1 h 220 mg PP, M_(w)˜5000 no change 24 h 245 mg PP, M_(w) ˜5000 no change 72 h 250 mg PP,M_(w) ˜5000 no change

[0194] This experiment indicates the following:

[0195] After only about 1 hour, virtually all soluble material has beenleached from the filter.

[0196] The filter consistency is maintained even after long exposure tosolvent.

[0197] To avoid or minimize contamination of the solutions with lowmolecular weight PP, it is advisable to rinse the filters with puresolvent for about 1 hour before use (this was also done in the tests inexamples 1 to 4).

[0198] This method can make it possible to use even filter types whichare not totally stable for the preparation of solutions according to theinvention.

EXAMPLE 6 Storage Stability of Solutions Produced According to theInvention

[0199] To check whether the solutions produced according to theinvention can be stored for a prolonged period, the following experimentwas carried out:

[0200] A solution of polymer P-9 (polymer analogous to the polymers P-1to P-7; preparation of the solution in toluene in a manner analogous toexample 1) was dispensed into a 1 l bottle from ATMI Packaging(NOW-NP-01-A-GC). This bottle was placed in an aluminized PE bag(ALDRICH # Z18340-7), the bag was filled with argon and welded shut. Thebottle was stored at room temperature in a solvent cabinet. At definedintervals (cf. table 8), a small sample was taken from this bottle in aclean room, and this sample was examined to determine the concentration,viscosity and use properties in a PLED. The bottle was subsequentlyresealed. The results obtained are summarized in the following table.TABLE 8 Storage stability of a toluene solution of polymer P-9 producedaccording to the invention. EL data²⁾ Viscosity max. U [V] Ref. Ref.Sequential conc. at 40 s⁻¹ eff. at 100 eff. U number Day¹⁾ [g/L] [mPas][Cd/A] Cd/m² Cd/A] [V] #1  0 5.19 13.8  9.82 3.3 10.2 3.4 #2  30 5.1213.5 10.77 3.3 10.5 3.6 #3  59 5.05 13.5 10.10 3.7 10.7 3.5 #4  86 5.2514.4 10.43 3.2 10.4 3.6 #5 122 5.12 14.3 10.40 3.4 10.9 3.5 #6 147 5.1715.0 10.10 3.4 11.2 3.4 #7 175 5.14 14.3  9.80 3.4 10.0 3.6 #8 215 5.1214.5 10.20 3.4 10.5 3.9 #9 317 5.19 15.6  9.90 3.2  9.7 3.7 #10 390 5.2513.9 10.01 3.1 11.2 3.2 ø — 5.16 14.3 10.15 3.3 10.5 3.5

[0201] The results reported enable the following conclusion to be drawn:

[0202] within the limits of measurement accuracy, the solution of theinvention can be stored without changes in concentration, viscosity andusability for PLED production for more than one year.

1. A process for preparing solutions comprising polymeric organicsemiconductors, which comprises the steps: A) dissolution of at leastone polymeric organic semiconductor in a suitable solvent (STARTINGSOLUTION), B) after-treatment of the starting solution from step a)(SOLUTION), C) filtration of the SOLUTION from step b) by means ofdead-end filtration and/or crossflow filtration and isolation of thefiltered solution comprising at least one polymeric organicsemiconductor (FILTERED SOLUTION).
 2. The process as claimed in claim 1,wherein a mixture of a plurality of polymeric organic semiconductors(polymer blend), and optionally in combination with one or more lowmolecular weight additives, is used in step A).
 3. The process asclaimed in claim 1, characterized in that a solvent mixture is used instep A).
 4. The process as claimed in claim 1, wherein the polymericorganic semiconductor is dissolved in the solvent (step A) by action ofshear forces forces.
 5. The process as claimed in claim 1, wherein thesolution from step A) still comprises dispersion-like constituents. 6.The process as claimed in claim 1, wherein the after-treatment of thesolution from step A) is carried out by means of one or more mechanicalafter-treatment(s).
 7. The process as claimed in claim 6, characterizedin that the mechanical after-treatment is carried out by means ofultrasound, a fast-running, high-shear dispersing stirrer and/or adisintegrator.
 8. The process as claimed in claim 1, wherein thesolution obtained in step B) is prefiltered before the filtration instep C).
 9. The process as claimed in claim 1, wherein the solutionobtained in step C) is filtered by means of further filtration methods.10. The process as claimed in claim 1, wherein theconcentration/viscosity ratio of the FILTERED SOLUTION obtained in stepC) is adjusted by addition of solvent or solvent mixture.
 11. Theprocess as claimed in claim 1, wherein step A), step B) and/or step C),are carried out under an inert atmosphere.
 12. The process as claimed inclaim 10, characterized in that the filtration in step C) and theaddition of the solvent or the solvent mixture are carried out in aclean-room environment.
 13. The process as claimed in claim 1, whereinthe solution obtained in step C) is packaged in containers suitable forclean-room conditions.
 14. The process as claimed in claim 13,characterized in that the packaged solution is blanketed with an inertatmosphere.
 15. The process as claimed in claim 1, wherein theafter-treatment in step B) reduces the molecular weight of the polymericorganic semiconductor.
 16. The process as claimed in claim 1, wherein adeep bed filter and/or membrane filter is used in step C).
 17. Asolution of polymeric semiconductors which is prepared as claimed inclaim
 1. 18. cancelled
 19. cancelled
 20. cancelled
 21. A polymericorganic light-emitting diode (PLED), organic integrated circuit (O-IC),organic field effect transistor (OFET), organic thin film transistor(OTFT), organic solar cell (O-SC) or organic laser diode (O-laser)produced using a solution as claimed in claim
 17. 22. The process asclaimed in claim 4, wherein the polymeric organic semiconductor isdissolved in the solvent (step A) by stirring or mixing, and optionallywith heating.
 23. The process as claimed in claim 1, wherein all stepsA), step B) and step C) are carried out under an inert atmosphere. 24.The process as claimed in claim 11, wherein the filtration in step C)and the addition of the solvent or the solvent mixture are carried outin a clean-room environment of class
 100. 25. The process as claimed inclaim 11, wherein the filtration in step C) and the addition of thesolvent or the solvent mixture are carried out in a clean-roomenvironment of class
 10. 26. A process for producing layers of polymericsemiconductors which comprises using the solution as claimed in claim17.
 27. The process as claimed in claim 26, wherein the process is acoating process.
 28. The process as claimed in claim 27, wherein thecoating processes is a doctor blade coating, spin coating, meniscuscoating, transfer printing, ink jet printing, offset printing or screenprinting process.